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Mycobacterium leprae was apparently the first bacterium to be identified as causing disease in humans. The year was 1873. The disease was leprosy, also known as Hansen’s disease. Despite popular belief, leprosy doesn’t make your arms and legs fall off. But if left untreated, it can cause permanent damage to the skin, nerves, limbs and eyes, to the point were the person does not realise they have inadvertantly injured themselves (say by picking up something boiling hot). It is these kind of injuries and secondary infections can then lead to tissue loss, especially of fingers and toes. I once heard a leprosy researcher say one of the greatest innovations in leprosy treatment was providing sufferers with shoes of some sort.

24 year old man from Norway, suffering from leprosy, circa 1886. From Wikipedia.

M. leprae is related to the very slow-growing bacterium that causes tuberculosis, but is even more difficult to work with. Scientists still haven’t identified the correct nutrient mix to grow M. leprae in the lab, instead they have to be grown in the footpad of a mouse or by infecting a nine-banded armadillo. Seriously.

The niche for M. leprae is the Schwann cell, a really important non-neuronal cell type that keeps peripheral nerve fibres alive. A paper just out in the Elsevier journal Cell (alas, it is behind a pay wall) shows that M. leprae can effectively reprogramme Schwann cells, making them more stem cell like. According to Toshihiro Masaki, Anura Rambukkana and colleagues from the University of Edinburgh and Rockefeller University, New York, these infected reprogrammed Schwann cells were capable of turning into various cell types, including muscle and bone which were then incorporated into skeletal and smooth muscles. This answers the question of how M. leprae spreads to these tissues in the later stages of infection. The authors also found that the infected ‘stem-cell like’ Schwann cells also secreted a cocktail of chemicals that attracted macrophages to them. By then infecting these macrophages, M. leprae was able to spread even further around the body.

The big hope now is that scientists can learn some new tricks from M. leprae to help them make stem cells in the lab, as well as gaining a better understanding of how Schwann cells can be reprogrammed. Wouldn’t it be ironic if the cause of an often neglected infectious disease ends up unlocking some of the mysteries of stem cells?